The present invention relates to an industrial robot wrist unit, comprising a wrist housing, which is intended to be fixed on a distal end of a robot arm and which has two fork arms between which a tilt housing is pivotally mounted, the tilt housing supporting in turn a rotatably mounted turn-table, on which there can be mounted a distal implement, in the wrist housing there being rotatably mounted first and second drive shafts, the first drive shaft, via a first and a second gearing, being able to rotate the turntable about a first axis and said second drive shaft, via a third gearing being capable of pivoting the tilt housing about a second axis which crosses the first axis.
In previously known wrist units of the above mentioned type, the gearings have been mounted in the wrist housing so that reactive forces arising in the gearings during certain operating conditions have been able to force the fork arms apart in an undesirable manner to the detriment of the precision in positioning the tool mounted on the turntable. This can be avoided by increasing the dimensions of the wrist housing, which has, however, caused an undesirable increase in weight in the entire wrist housing.